Silane-modified polymers have generally been known for many years, and sealing materials or adhesives based on silane-modified prepolymers or polymers have proved to be successful for a very wide variety of applications, for example in seam sealing in automotive construction, in windows or in the structural facings sector.
Very generally, silane-modified polymers (which are in the form of prepolymers prior to processing) are understood as being polymers which comprise silane groups having hydrolysable radicals and the polymer backbone of which is not composed substantially of O—Si—O—Si chains, as is the case with silicones, but of C—C chains, which in most cases are interrupted by heteroatoms and further comprise urethane, ether, ester, urea, amide and other structural units. Under the action of moisture, the radicals on the silane groups, for example usually acetate or alkoxy groups, are hydrolysed with the formation of reactive silanols, which subsequently condense and cure, with water, alcohol or acetic acid cleavage, to form a high molecular weight network.
The value of these silane-modified polymers is substantially their particular property profile. On the one hand, coating materials, adhesives or sealing materials that comprise silane-modified polymers are distinguished by strong adhesion to a very wide variety of substrates without complex pretreatment (no primer is necessary). This is because OH groups are normally present on inorganic substrate surfaces and are able to react with the reactive silanols of the polymer, which form under the action of moisture. On the other hand, the properties of the silane-modified polymers can be adapted to a large number of very different applications with the aid of the polymer backbone.
The silane-modified polyurethanes and polyureas that are currently available commercially on the market are thus based on a high molecular weight backbone which is produced (i) by reaction of NCO-containing prepolymers with aminosilanes or (ii) by reaction of OH-terminated prepolymers, such as, for example, polyethers, polyurethanes or polyesters, with NCO-functional silanes, as is shown in the following formula scheme:

A disadvantage of coating materials, adhesives and sealing materials that are based on silane-modified polyureas is, however, the high viscosity of their prepolymers. On account of the high viscosity, the use of silane-modified polyureas is possible to only a limited extent, because the coating or sealing materials to be used must normally be applied in the liquid to pasty state to the substrate parts that are to be coated or adhesively bonded. A prepolymer that is too viscous is consequently difficult or impossible to use as a coating material, adhesive and/or sealing material.
Furthermore, the degree of hardness of the resulting coating, adhesive bond and/or seal as the end product after the silane crosslinking is critical for the particular use in question. In the case of silane-modified polyureas, end products having a high degree of hardness are normally obtained. Silane-modified polyurethanes, on the other hand, provide, softer end products after curing. However, the synthesis of silane-modified polyurethanes having a high silane content is difficult to carry out economically because of the relatively expensive NCO-functionalised silane precursors.
The monomeric NCO content in silane-modified polymers additionally plays an important role in this connection: on account of the not negligible vapour pressure of the isocyanates (even at room temperature), isocyanate vapours that can be harmful to health or at least sensitising can form even during spray application. Consequently, the development of reactive prepolymers which are substantially free of isocyanate monomers and in any case are below the exposure limit value (Total Reactive Isocyanate Group concentration TRIG) according to the Technical Rules for Hazardous Substances (TRGS) 430 (edition March 2009) of 0.018 mg/m3 NCO, preferably below 0.01 mg/m3, particularly preferably below 0.001 mg/m3, is desirable.